Study: Zebra Stripes Deter Horseflies

According to a recent study, a coat pattern with numerous narrow stripes deteres horseflies from landing.

Photo: Photos.com

Zebra stripes might soon be the new hot fashion in summer equine wear. Printed on rugs and sheets, ear covers, and leg wraps, it could be attractive to everyone.

Everyone, that is, except horseflies.

That's because, according to a recent study by Hungarian and Swedish researchers, horseflies--known to scientists as tabanids--find zebra stripes incredibly unappealing. And the thinner and more numerous the stripes, the more the flies are deterred from landing on the animal.

"We conclude that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure a minimum attractiveness to tabanid flies," said Gabor Horvath, PhD, researcher at the Environmental Optics Laboratory in the Department of Biological Physics at Eotvos University, in Budapest, and chief author of the study.

This finding could be particularly beneficial for owners of black or brown horses. Dark horses attract significantly more horseflies than light-colored horses and zebras, Horvath said.

It all comes down to a question of light polarization. Polarization describes the way the electric vectors in light waves move in certain distinct patterns. While humans can't detect that polarization, tabanids can. Considered "polarotactic," horseflies are very attracted to certain kinds of polarization. The horizontal polarization of water-reflected light, for example, leads them to water sources where they can mate, reproduce, and rehydrate. Linear polarization leads blood-sucking female horseflies to food sources such as equids and cattle.

Dark colors on large animals reflect strong linear polarization, attracting nearby polarotactic female horseflies to come to the dinner table. Light colors, on the other hand, produce weak polarization. But when the dark and light colors are striped together in zebra format, the polarization signals blend and confuse tabanid eyes, Horvath said, and they tend to turn and fly the other way.

"The darkness of a horse's coat is a disadvantage (for horsefly protection), which was recognized only after our experiments," Horvath explained.

In his team's experiments, they placed various platters filled with vegetable oil in a fly-infested Hungarian pasture. Each platter was painted in different patterns of black and white stripes or painted all black or all white. Black platters caught the most flies in the oil, and platters with the thinnest black and white stripes caught the fewest. According to Horvath, this pattern resemble that found on the legs and faces of zebras.

The researchers ran a similar test on three-dimensional plastic horse models placed in the field, painted black, brown, white, and zebra-striped and covered in sticky glue. Over the course of 59 days, the black horse caught 562 horseflies; the brown horse caught 334; the white horse caught 22 horseflies; and the zebra model caught only eight.

Zebra striping might be useful in some horse breeds today, Horvath said. Some mustang herds, for instance, with zebra striping on their legs and dorsal stripes on their backs (such as the Gila and Kiger mustangs) could be benefiting from horsefly protection.

Unfortunately these conclusions are not black and white, so to speak. Polarization is only part of the attractiveness aspect. According to Horvath, movement and smells also play a critical role in attracting horseflies. A new study is under way to compare these additional factors, he said.

In the meantime, horse owners wanting to protect their equine friends from horsefly attacks might consider dressing them up as zebras--even if the fly season doesn't coincide with Halloween. "In the tabanid season (which peaks in summer), horsekeepers could protect their black and brown horses from biting tabanids with the use of white or even zebra-striped coverings," Horvath said. "A zebra-striped horse rug would be ideal."

New, patented, commercial horsefly traps that attract horseflies with high levels of linear polarization are also currently under development and testing in Hungary, based on this research, Horvath said.

About the Author

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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